To optimize message transmission, myelin, a fatty substance, coats the long axonal region of a neuron, speeding up signaling and insulating the axon from extraneous electrical or chemical impulses. A breakdown in myelin exposes the axon to misdirected electrical impulses. When diverted to unintended neurons, extraneous impulses can have devastating mental and physical consequences. Multiple sclerosis is caused by progressive degeneration of myelin.
Different regions of the brain become heavily myelinated during pre-programmed sensitive periods, which opens up windows of opportunity for developing specific skills or competencies. After a region is myelinated, a performance permanence sets in. Language-learning is one example. Every brain begins life with the capacity to learn any of the 6,000 languages spoken on Earth. When a child consistently hears the regular sounds (phonemes) in a given language, neural connections are created in the auditory cortex. The “window” for language-learning closes with the onset of puberty. Afterward, learning a new language will be more difficult and will typically be accompanied by a noticable accent.
Pruning the Garden of the Brain
Synaptic proliferation is the prenatal overproduction of synapses that gives a young brain its incredible adaptability. We are born with many more connections than our adult brains will use. This neural insurance policy guarantees that infants born in San Francisco, Shanghai or Soweto can flourish with equal ease. In the first two decades of life, the human brain “prunes” away connections in a dynamic self-reorganization that operates by the use-it-or-lose-it principle.
There is an old story about a man who walked from his farmhouse to his barn every day. After following the same path day in and day out, it wore into a groove. Eventually, the old man could walk to the barn blindfolded, since the deep channel would steer him directly where he was going. Neural pathways in the brain follow a similar pattern: They are strengthened with repeated use, while neglected networks become unreliable and eventually are pruned away.
Pruning helps the brain protect itself from devoting precious resources to useless networks and inefficient over-wiring. Apoptosis, programmed cell death, eliminates unneeded neurons, just as roads that are seldom traveled fall into disrepair and eventually are closed down for good. Unused skills suffer a similar fate: what we call “forgetting.” (While memory failures are generally due to degraded neural networks, accelerated memory loss is associated with stress, aging or acute brain damage.) Decreased use of skills reduces the nourishment of their networks, diminishing memory and performance.
In the absence of nearby land, some tadpoles will arrest the natural process of metamorphosis into frogs, because environmental conditions suggest that such a change is by no means beneficial to survival. Instead, those tadpoles remain swimmers. It is an apt metaphor for the developing brain.
Mother Nature offers a trade-off: instinct or flexibility. Those species whose behavior is dominated by instinct — e.g. reptiles, fish, amphibians, and insects — have brains that leave little room for neuroplasticity but are highly efficient. As a result, they are less adaptable. Human brains, on the other hand, were shaped by evolutionary pressures that rewarded adaptability. One example of our flexibility is the way our brains accommodate stimuli in multiple patterns and formats, but still accept them as the same object (See Chart 3: The Letter A).
Early Brain Growth
Neurogenesis is the rapid production of brain cells in utero, when neurons are produced at the incredible rate of 250,000 to one million per minute. The rapid growth of the young brain system begins 18 days after fertilization. The brain develops quickly through first-hand experiences. Computer simulations and early-learning videos are no substitute for the real world. A mere picture of an orange short-changes the learner, who cannot directly experience its smell, texture, taste and mass. Learners create meaning from what they do in their world, not from exposure to its representations.
While genetics and prenatal influences may calibrate the brain at birth, it is largely dependent on subsequent experiences to determine its capacities and deficiencies. Author Joseph Epstein stated, “We are what we read.” Neuroscientists would assert, “We are what we experience.” Neural circuits are constantly reorganized and rerouted, based on the quantity, quality and timing of our experiences. This has profound implications for what we should do in every home and school.
The stimulation young children receive from early interactions determines how their brains develop in the crucial postnatal period, when experiences have a decisive impact on the brain’s architecture and later capabilities. Brain cells create connections each time we integrate something new. Whether we are learning to crawl or dance, these experiences create brain pathways that capture what we know and who we are.
In its early years, the brain goes on a connectivity binge. The immature brain quickly links hundreds of millions of neurons together, forming efficient brain circuits (See Chart 4: Neural Connections). During these stages, children make learning look easy. By adding, removing, or changing the strength of the connections among neurons, linking cells together or eliminating brain cells from existing neural pathways, neuronal activations change, making specific new learning possible. The word specific must be underscored here. All learning must be specific and transferable if it is to have any currency.
Creating new neural pathways is physically exhausting. The infant brain requires near-constant feeding to keep up with the energy consumption necessary for early brain development. Infants tax their energies when they are learning how to walk, talk, think, speak and remember, along with familiarizing themselves with all of the people, places and objects in their environment. Toddlers must also learn the complexities of language, and must master critical cultural and socialization skills. All of these are the minimum challenges that must be successfully and simultaneously met for adaptation to the environment. Synaptic connectivity maxes out during the second year of life. At its peak level, each neuron averages 15,000 connections. That number occurs in the early years of child development, when a toddler’s brain consumes 225 percent of the energy of an adult brain.
Enrichment studies have shown that a caring environment aids learning and development. But neuroplasticity also has a darker side. Impoverished environmental conditions, prenatal substance exposure, sensory deprivation, emotional trauma and nutritional deficiencies can cause plasticity to play its unkind hand, wreaking havoc on the developing young brain. Long-term chronic stress (“toxic stress”) provokes the release of high levels of the hormone cortisol that can lead to permanent damage to hippocampal neurons, causing learning difficulties and memory impairments.
On the brighter side, the human brain responds favorably to emotional support, challenge and steady constructive — it need not always be positive — feedback by increasing the myelination and nourishment of neural pathways. Individuals who are blind at birth have highly resilient brains eager to compensate for any deficiency. With their acute hearing ability, some of the world’s best musicians have emerged among the blind. In the absence of appropriate stimulation, the brain reassigns underutilized areas for other, sometimes completely different, functions.
Failure is not an option is a popular educational mantra that was unwisely borrowed from the business world. It inaccurately reflects how the young human brain learns. Students who struggle in school often appear to be impervious to the best efforts of well-trained professionals. The notion of “rigor” becomes almost academic rigor mortis for them. In nearly all cases, each learning difficulty is indicative of a neurological underinvestment in the necessary brain wiring needed to be successful. When we point to a concept or skill that is not “developmentally appropriate,” the reference we are making is to brain development, not curriculum development.
With this backdrop, certain academic shortcomings are expected. However, these events foster frustrations when the child “doesn’t get it.” With time, maturation and the appropriate brain wiring, s/he will one day “get it.” When it comes to learning, failure is often a prerequisite. This is particularly true when learners lack related prior experiences, as the new information cannot merge with brain circuits that don’t exist yet. When there is nothing with which to integrate new knowledge, the building process must begin from scratch. The child is not “slow”; the process of brain-building is sometimes slow.